1. Field of the Invention
The present invention relates generally to products and methods for preventing electro-magnetic interference. More particularly, the present invention relates to a conductive and arbitrarily strong radio frequency (RF) shield that protects electronic equipment from being disrupted by RF waves while also allowing for fluid or air flow therethrough, and a method for making the RF shield.
2. Description of the Related Art
For many years, it has been known that electro-magnetic fields, such as RF waves, can disrupt the operation of electronic equipment and cause electronic equipment to malfunction. For example, the RF energy radiated from a nearby lightning strike, sometimes referred to as an electro-magnetic pulse (EMP), can disrupt sensitive electronic equipment or RF from a vacuum cleaner motor can disrupt a television. It is well known that conductive shielding can be effective in preventing RF waves from penetrating a given volume. Therefore, conductive shielding (RF shielding) has been implemented to protect electronic equipment.
The classic RF shield is called a “Faraday cage,” which is a conducting cage or perimeter that conducts electromagnetic energy on its surface so that electro-magnetic radiation from outside of the cage will be distributed on the outer surface of the Faraday cage and will not pass through the cage into the interior, thus preventing disruption to any equipment within the cage. Faraday cages are often used to shield sensitive electronic or electro-mechanical equipment. The cages can be made of a solid conductor and fabricated in many shapes and sizes, and used in combination with other shields.
Often, there is a need to provide for openings in RF shielding to allow for fluid or air flow from outside the shielding to the inside or to provide visual access to the interior. For example, electronic equipment may require ventilation, electro-mechanical equipment may need to be able to receive coolant and to vent exhaust, or human operators working within a protected volume may require HVAC. Examples of such applications can include news vans, satellite up-links, aircraft cockpits, diesel generators, mobile switching stations and medical diagnostics laboratories.
A number of solutions have been offered to address the above-problem. For example, metallic screens have been proposed and implemented. Such screens can be found on the doors of home microwave ovens. Metallic screens also form the walls of the classic “screen room” which can provide adequate shielding for some applications while being somewhat transparent and provide for ventilation. However, metallic screens provide quite limited RF attenuation and are structurally weak.
“Honeycomb” shielding, such as silver-soldered and brazed-foil honeycombing attenuates RF energy better than screens. Honeycomb panels are formed by folding strips metal foil into a crenulated pattern then bonding them together forming hexagonal or square apertures. Honeycomb shielding is still relatively delicate and is not strong enough to handle stresses in many circumstances, such as in a vibrating environment (e.g., a moving vehicle, a pulsating flow, etc.).
A third type of shielding, called a “tube pack”, is formed by seam welding a plurality of metal tubes together. This type of shielding provides the shielding effectiveness of honeycomb panels, is mechanically much stronger than screens or honeycomb panels, and can be used in a number of applications where screening or honeycombs cannot. The principal disadvantages of “tube packs” are their fabrication complexity with all the joints having to be seam welded, the volume taken by the assembled “tube pack”, and in some cases the weight of the assembly.
In the examples noted above both the honeycomb panels and the “tube packs” can provide adequate RF shielding; for many applications the metallic screens cannot. Honeycomb panels are not structurally strong enough to hand hostile environments. Tube packs can be structurally strong but require a considerable volume and weight allocation and are very expensive to fabricate.
Thus, there is a need for improved RF shields that can be made arbitrarily strong and withstand harsh environments that impose, for example, consistent vibration, corrosion, extreme temperature and other stress inducing conditions and yet be compact and lightweight compared to the alternatives.